Center pivot irrigation systems are widely used for the irrigation of large agricultural areas. A center pivot system consists essentially of an elongated conduit which has one end fixedly secured at a center pivot around which the conduit is driven by a series of drive towers. Water is pumped into the conduit at the center pivot and exits the conduit through a plurality of sprinklers spaced along its length. The length of a commercial system of this kind may range from about 200 feet (61.0 meters) to over 1500 feet (457.2 meters). In any such system, because the inner portion of the radially extending conduit moves much more slowly than the outer portion, it is necessary and customary to provide for a substantially larger discharge of water at the outer end of the system than at the inner end. This control may be exercised in various ways as is known in the art including providing sprinklers or discharge nozzles with an orifice size varying from the inner end to the outer end in relation to the rate of water flow desired, or some type of programmed time control using discharge nozzles of uniform size, or some other method.
The conventional center pivot irrigation system covers a circular area out of what may be a rectangular or square field, leaving the corners unirrigated and also uncultivated. One of the ways that has been developed to at least partially irrigate the corners of a rectangular or square field has been to provide long distance sprayers or end guns mounted at the end of the conduit for spraying the water into the corner area as the conduit sweeps the adjacent central or primary area. The normal mode of operation calls for the end gun to be off when the outer end of the conduit is adjacent the edge of the field and on when the conduit sweeps adjacent a corner area or other odd shaped area. The control for the end guns is usually provided by some combination of switches and cams mounted at the center pivot which turns on the end guns as the system approaches the corner and off after the system has passed through the corner.
In the past, the use of end guns has been somewhat limited due to the water pressure balance problems experienced in the conduit when the end guns are cycled on and off as well as the maximum flow rate and pressure of the water supply which limits the effective operation of an end gun mounted at the extreme end of the system. A tremendous drop in pressure and flow rate is experienced along the conduit as the end guns are turned on, the end guns usually requiring a much higher pressure and flow rate than the nozzles along the conduit. This is especially a problem for the longer range end guns which spray up to twice as far and cover much greater areas than the short range end guns.
Some systems in the prior art use various combinations of short and long range end guns with their standard center pivot irrigation systems but these systems utilize sequencing operations requiring multiple sweeps or alternate starting and stopping beyond that normally used for controlling average speed in an effort to achieve an equal watering throughout the center circular area as well as the additional area beyond the periphery of the circle. In one of these systems, a short range and a long range end gun are mounted near the outer end of the conduit and are operated in one of two modes each requiring two or more sweeps to complete an irrigation cycle.
In the first mode of operation, the complete system must sweep through the field twice to complete an irrigation cycle. During the first sweep, the short range end guns are sequenced on during a first and last portion of sweep through the corner. During a second sweep, the conduit travels at 100% speed except for the middle portion of the corners. For its sweep through this section, the nozzles along the entire length of the conduit are turned off and the long range end gun is turned on to irrigate that portion of the field beyond the periphery of the circular area not irrigated during the first sweep. The speed of the conduit is set for approximately three times the speed used when the short range end guns are on as the long range end gun has an application rate of about three times that of the short range end guns.
There are several inefficiencies encountered in a system using the sequencing mode described above, including a watering imbalance between the corner areas and the central circular area, and application rates which vary widely between that of the long range end gun and the conduit discharge nozzles. Furthermore, the sequence requires at least two sweeps through a field which may be as much as a full 24 hours longer than one sweep.
In a second mode of operation, the same system may utilize four sweeps through the field in an attempt to equally water corner areas as well as the central circular areas. In this mode, the first three sweeps may be the same as the first sweep in the other mode of operation in that the short range end guns are turned on when the conduit sweeps through a first and last portion of the corner area. The long range end gun is not cycled on. For the fourth sweep through the field, the conduit operates much as in the second sweep of the previous mode in that the conduit travels at 100% speed but slows to the same speed that was used for short range end gun operation for its sweep through the middle portion of the corner. During its sweep through the middle portion of the corner, the long range end gun is cycled on and the nozzles along the length of the conduit are cycled off so that all of the water is diverted for operation of the long range end gun. As the long range end gun applies water at about three times the rate of the short range end guns, one sweep with the long range end gun will apply approximately the same amount of water as that applied by three sweeps with the short range end guns on.
This mode of operation provides a better balance of water throughout both the corner and the center portion of the field, but there still exists an imbalance because the center conduit must be turned off during its sweep through the middle portion of the corner to operate the long range end gun. Furthermore, the middle portion of the corner receives an excessive amount of water by the long range end gun as it must receive water equal to that received by other areas of the field during three or four sweeps of the conduit. This produces a large amount of run-off and inefficient irrigation as compared with a more balanced application rate as experienced by other portions of the field. Also, the time required to complete a full cycle of irrigation is four sweeps and not two as in the previous mode which may be as much as three days longer than that required to sweep through the field one time.
Another system which utilizes a short and long range end gun in combination with a center pivot conduit has a somewhat different sequencing method for irrigating a corner area. During a first part of the corner, a short range end gun is cycled on. During a large middle portion of the corner, the system operates in two alternate modes. The conduit will move for a short distance with the short range end gun on to irrigate partway into the corner, and then the conduit will stop, all the discharge nozzles along it will be turned off, and the long range end gun will be cycled on for a period of time to irrigate a portion of corner area beyond that irrigated by the short range end gun. The conduit will then start up again and will travel to another stopping point, with the short range end gun and the nozzles along the conduit on in between the two stopping points. There may be as many as ten stopping points through the middle portion of the corner to provide for an adequate amount of water to be delivered to the area beyond the short range end gun's reach. The system operates through the last portion of the corner as it did in the first portion, with the short range end gun on.
This mode of sequencing has inefficiencies due to the continual starting and stopping of the system which greatly increases the mechanical wear and tear, control system requirements, and maintenance problems. Furthermore, there must be a great deal more of overlap between the sprinkling patterns of the end guns as the short range end gun is used to irrigate between the central area and that area irrigated by the long range end gun. This, in addition to the multiple stopping of the system at selected locations requires that the watering patterns overlap much more than in a continually moving system to ensure that there are no areas which receive little or no water. Also, the time required for one sweep through the field is increased over that of a system which moves continuously through the field, although not as greatly as in the other systems.
Applicant has developed a system for balancing the water pressure and flow rate between the center pivot conduit and the end guns and which provides for an even distribution of water and application rates throughout both the area included within the arc as well as the area sprayed by both the long range and short range end guns. In addition, applicant's system utilizes a sequencing mode which equally irrigates all parts of the field with each sweep of a continuously moving conduit. It is to be understood that by "continuously moving" is meant that the conduit is always moving at an average speed in a manner customary in the art for controlling the normal operation of a center pivot irrigation system. It does not mean that the conduit is always moving at every instant of time as it is customary to control the average speed of a conduit by alternately stopping and starting a selected one or more of the control towers such as by use of a percent timer or the like. But, the system of the present invention is moving continuously at some average speed in the sense that the system is not made to stop at selected locations while one or more end guns operate.
In applicant's system, the sprinklers along an outer section of the conduit are turned off to increase the water pressure and flow available for use by the longer range end gun. By turning off this portion of conduit, applicant's system provides water at a sufficient pressure and flow rate to effectively operate the long range end gun at something less than maximum range. However, applicant's system at the same time continues irrigation along the majority of the conduit which eliminates the inefficiencies of the systems in the prior art. To compensate for the section of conduit that's off, the watering pattern of the longer range end gun is adjusted so that it sprays inwardly of the arc to irrigate the area normally swept by the outer section in addition to a substantial area beyond the arc and into the corner. This is made possible by the relatively greater capacity of the end gun as compared with the standard nozzles of the conduit. A typical long range end gun delivers approximately three times the water delivered by a section of conduit over equal areas. In applicant's system the spray pattern of the longer range end gun is adjusted to provide about two thirds of its spray beyond the outside of the arc and only about one third along the inside of the arc to balance the delivery of water.
Thus, a center pivot irrigation system may be provided with a short and long range end gun at its outermost end which will continuously irrigate an inner area as well as provide for the irrigation of land along two different ranges beyond the central arc with a balanced application of water and without the need to start and stop the conduit at selected locations or miss complete sections of land during a single pass of the system through the field.
As the watering pattern for end guns may be erratic in that they tend to distribute more water towards the periphery of their spray pattern, auxiliary sprinklers may be provided along the outer section of conduit to fill in any inconsistencies in the long range end gun coverage. These auxiliary sprinklers are generally very few in number and do not significantly reduce the amount of pressure and flow rate available for the longer range end gun.
Another feature of applicant's system is that it can be added to an existing center pivot system or supplied on new systems by the use of an existing control wire extending from the central pivot out to the periphery of the conduit where the end guns are mounted. This is important as the conduit may be up to 1500 feet (457.2 meters) long and extra wires would be substantially more expensive to supply and connect. With the one wire, applicant can operatively electrically select one of two ranges of end guns for operation in various parts of the corner area. This provides increased capability for spraying as one or more shorter range end guns may be used to fill in areas which could not be properly covered by a longer range end gun and a longer range end gun can be used to reach beyond the range of a short range end gun. A second short range end gun may be provided to increase the irrigation rate and improve the coverage.